Why, in Vayikra 21:10, does the verse state "...HaGadol MeEchav" instead of simply "HaGadol"?

Question

In this weeks Parsha, Emor, I came across this pasuk:

והכן הגדול מאחיו אשר יוצק על ראשו שמן המשחה ומלא את-ידו ללבוש את-הבגדים את-ראשו לא יפרע ובגדיו לא יפרם:‮
_{(ויקרא כא:י)}

And he that is the high priest among his brethren, upon whose head the anointing oil was poured, and that is consecrated to put on the garments, shall not uncover his head, nor rend his clothes.
_{(Vayikra/Leviticus 21:10; translation source)}

This caught my eye, because of the word "מאחיו" - why is this word here? Looking through a copy of the קונקורדנציה (concordance), it seems like this is not a common thing - that in most places it's simply הכהן הגדול.

Why include the word "מאחיו" here?

Answer 1

Sifra (halakhic midrash to the book of Vayikra) seems to pick up on this unusual phrasing, and derives from it laws regarding the status of the Kohen Gadol and his relationship to the other kohanim.

Sifra comments on the verse in question as follows:

והכהן הגדול מאחיו שיהא גדול מאחיו בנוי בעושר בכח בחכמה ובמראה. אין לו מנין שיגדלוהו משל אחיו? תלמוד לומר הגדול מאחיו שיהא גדול מאחיו

"And the priest who is greater than his brothers" - he should be greater than his brothers in beauty, wealth, strength, wisdom and appearance. If he is not, how do we know that he is to be elevated from his brothers' property? The Torah states, "greater than (lit. from) his brothers", that he should become great from his brothers.

The midrash goes on to discuss the case of a poor Kohen Gadol whose brother kohanim contributed funds to make him wealthy.

Answer 2

GEMARA YOMA 18a (גמרא יומא, דף י"ח, עמוד א).

והכהן הגדול מאֶחיו, אשר יוצק על ראשו שמן המשחה ומילא את ידיו ללבוש את הבגדים". "שיהא גדול מאחיו בכוח, בנוי, בחוכמה ובעושר. אחרים אומרים: מנין שאם אין לו [כסף] שאחיו הכהנים מגדלין אותו? תלמוד לומר: והכהן הגדול מאחיו - " גדלהו משל אחיו:

And the priest that is highest among his brethren, that means he should be highest among his brethren in strength, in beauty, in wisdom, and in riches. Others say: Whence do we know that if he does not possess [wealth], his brethren, the priests, endow him? To teach us that it says: ‘And the priest who is great [by reason of] his brethren’, i.e., make him great from what his brethren have: